This invention relates to means for preventing taint of copying papers caused during operations of an electronic copying machine which is provided with a fixing roller and a roller subsidiary to said fixing roller, the subsidiary roller diffuses offset preventives throughout the whole cylindrical face of said fixing roller.
Heretofore, means have been known for diffusing offset preventives--silicone oils are mostly used--throughout the cylindrical face of the aforesaid fixing roller by means of a subsidiary roller kept in contact with said fixing roller. In FIG. 2, the aforesaid fixing roller is indicated at "a" and said subsidiary roller in contact with said fixing roller "a" is indicated at "b". Also, in FIG. 2, "c" is a heating roller, "d" is an oil applying roller, "e" is an oil feeding roller, "f" is a felt wick, "g" is an oil reservoir, and "h" is a guide plate for copying papers.
However, in cases where said rollers a and b along the lengths of the same are different from the width of a copying paper in use, oil, due to absorption of oil by said paper, is accumlated at the end portions of said fixing roller with which portions the paper does not come in contact. Therefore, when using a copying paper which is larger in width than the paper which had been fed in the prior copying operations, taint of said new larger paper at the edge portions thereof cannot be avoided.
In view of the above-noted shortcoming in successive copying operations in which copying papers having different widths are used, a roller having an oil absorbing layer has been proposed for the aforesaid subsidiary roller. Such a newly proposed subsidiary roller has been disclosed, for example, in Japanese Published Unexamined Patent Application No. 55-101975. This prior art subsidiary roller has an oil absorbing layer such as made of a paper web or of foamed urethane rubber is shown in FIG. 1 in which such an oil absorbing layer is indicated at "k".
However, the aforesaid shortcoming can hardly be avoided in a comparatively short period of use even when the subsidiary roller having an oil absorbing layer is used. It has now been determined that such an undesirable phenomenon is caused by the fact that the oil absorbing layer of said subsidiary roller becomes saturated with oil far more rapidly at the end portions of said layer than at the middle portions of the same layer. Said end portions of said layer correspond to the end portions of the fixing roller with which copying papers have not been in contact, and said middle portions of said layer correspond to the middle portions of the fixing roller with which portions of said copying papers have been in contact. So, capability to remove oil is lost rapidly at the end portions of said layer.